1. Field of the Invention
The present invention relates to a motor driving device for a sewing machine, and more particularly relates to a motor driving device for a sewing machine including a machine motor fixed to the machine frame, wherein tilt of the machine frame is detected to control the drive of the machine motor.
2. Description of Related Art
In an industrial tiltable sewing machine of this type, a machine frame constructed of an arm and a bed is placed on a table. The bed is pivotably supported at its rear portion to the table, so that the machine frame can be tilted with respect to the table. In adjusting various devices provided within the bed, e.g., a fabric feeding device, a thread cutting device and a rotating hook, or adjusting tension of a timing belt wrapped on a lower shaft in the bed, the machine frame is tilted rearwardly to open a bottom portion of the bed. That is, such an adjustment is carried out when the machine frame is in a tilted condition. As such a sewing machine having the above construction, there is known a direct drive type sewing machine including an upper shaft and a motor shaft directly connected to one another in the arm of the machine frame. This type of sewing machine is provided with a foot switch for controlling driving and stoppage of the machine motor. However, if the foot switch is erroneously depressed during the adjustment as mentioned above under the tilted condition of the machine frame, the machine motor begins to be driven. As a result, a needle begins to be moved, thus causing a danger.
As a countermeasure for solving this problem, there is disclosed in U.S. Pat. No. 2,833,235, for example, a sewing machine including a tilt sensor for detecting the tilt of the arm or the machine frame. When the tilt of the machine frame is detected by the tilt sensor, the machine motor is inhibited from being driven even if the foot switch is depressed, thus improving the safety of the sewing machine.
In the above construction, when the machine frame is tilted, the machine motor cannot be driven at all. However, in adjusting various devices provided in the bed during the tilted condition of the machine frame, the adjustment may be performed more easily as the machine motor is driven. In this circumstance, it is demanded by a user or a customer engineer that the machine motor can also be driven when the machine frame is tilted.